The present invention relates to an electromagnetic injection valve having a double coil, in which a first and a second magnetic coil having the same characteristics are arranged on the same magnetic circuit, with one end of each magnetic coil being connected to the same supply voltage and the other end connected to a first and a second switching means, respectively, of an electronic drive circuit, and a holding circuit controllable by the drive circuit being parallel-connected to the first magnetic coil.
A conventional electromagnetic injection valve is described in Unexamined German Patent Application No. 2 306 007. In the conventional electromagnetic injection valve, two or more magnetic coils on the same magnetic circuit and an electronic drive mechanism functionally adapted to this arrangement are used to open and close the shutoff element of the injection valve by generating an electromagnetic attraction force opening the shutoff element from its closed state via a first excitation, generating an electromagnetic attraction force holding the shutoff element in its open state once it has been opened through a second excitation, and finally generating an opposite magnetic flux through a third excitation, thereby extinguishing the induced magnetic flux and closing the shutoff element from its open state.
As a general rule, the current increase in an electromagnetic injection valve, and thus also the force increase in an armature, is largely determined by the inductance and resistance of the valve coil and supply voltage Ubatt of the coil. The inductance is derived from the number of coil windings and the design of the magnetic circuit. In motor vehicles, the supply voltage is limited to 12 volts. Today""s turn-on time requirements for an electromagnetic injection valve used in a motor vehicle have led, in single valve coils, to very high currents that cannot be achieved with present switching transistors and existing line resistance values.
Up to now, the fast increase in current and force needed in the injection valve at turn-on has been achieved with a higher voltage from a booster capacitor that is charged by a d.c.-d.c. converter or by recharging. The d.c.-d.c. converter is needed in magnetic circuits with high eddy-current losses because recharging with the valve inductance is too inefficient in this case. In addition, recharging with the valve would lead to excessively long booster capacitor charging times. The recharging current excites the magnetic circuit, thus reducing protection against leakage and unwanted valve opening.
An object of the present invention is to provide a reliable electromagnetically operated injection valve with the shortest possible turn-on and turn-off times and simple circuitry.
In an electromagnetic injection valve according to the present invention, the object is achieved by winding the two magnetic coils in opposite directions so that their forces cancel each other out if the same excitation current flows through them, and by the drive circuit controlling the switching means during one complete open-hold-close cycle of the valve so that
during a first phase, an initial charging action occurs while the valve is closed, with both switching means being closed while the holding circuit is inactive, and the current flowing through the two magnetic coils rising at a relatively slow rate;
during a second phase, which is a valve opening phase, the current flowing through the second magnetic coil is quickly turned off as the second switching means opens, while the first switching means remains closed and the holding circuit remains inactive;
during a third phase, which is a holding phase, the holding circuit is activated, causing the current flowing through the first magnetic coil to drop to a holding current intensity; and
during a fourth phase, which is a closing phase, the valve is closed by at least deactivating the holding circuit and opening the first switching means.
The canceling action of the double coil transforms the actual valve activation, i.e., the valve opening action, into a turn-off action in one of the two coils in the second phase. The rapid current drop is then determined by dimensioning the extinction voltage. Rapid force rising times can therefore be achieved without increasing the supply voltage. The injection valve can be controlled by a conventional switching output stage or by a current-regulated switching output stage. Reversing the differential current at turn-off also makes it possible to shorten the closing action. One important advantage of the present invention is therefore the ability to simplify and reduce the cost of the output stage. No booster capacitor or d.c.-d.c. converter is needed in the control unit. As a result, it is also possible to easily integrate the output stage into the control unit.